Both cytokines and inflammation have been shown to rocket during depressive episodes, and – in people with bipolar – to drop off in periods of remission. Healthy people can also be temporarily put into a depressed, anxious state when given a vaccine that causes a spike in inflammation. Brain imaging studies of people injected with a typhoid vaccine found that this might be down to changes in the parts of the brain that process reward and punishment. There are other clues, too: people with inflammatory diseases such as rheumatoid arthritis tend to suffer more than average with depression; cancer patients given a drug called interferon alpha, which boosts their inflammatory response to help fight the cancer, often become depressed as a side-effect. - www.theguardian.com